1. Field of the Invention
This invention relates to data center energy usage and conservation management, and in particular, it relates to system and method for improving energy usage and conservation of air-management units in a data center utilizing a multiplicity of rack mounted power distribution units.
2. Description of the Related Art
Data centers are widely used in computer, networking and telecommunication and other related industries. A typical data center has one or more computer rooms where multiple racks are installed. Multiple electronic devices/appliances, computers/servers, networking and/or telecommunication equipment (collectively “electronic devices”) are mounted on each rack. Electrical powers to these electronic devices are provided through rack power distribution units (“rPDUs”). An rPDU is a rack-mount or rack-based device typically having multiple appliance outlets designed to distribute electric power to the multiple electronic devices mounted on the racks located within a data center.
In a typical arrangement, a computer room has a raised floor, upon which a multiplicity of racks are mounted or based. The computer room is often equipped with air conditioning units, commonly known as computer room air conditioners (CRAC) or computer room air handlers (CRAH) units, to control and manage the working environment inside the computer room. The CRAC/CRAH units are designed to achieve and maintain, for example, temperature and humidity levels, both inside the computer room and more importantly within the racks, within certain ranges that are suitable for the operating conditions of the electronic device mounted on the racks.
A typical CRAC/CRAH unit may include a chiller for chilling the air through a refrigerant or coolant and water, a dehumidifier for drying the air, and a fan for blowing the air for circulation. The CRAC/CRAH units can distribute cooling air through air conduits under the raised floor of the computer room, which often has perforated tiles placed in front or beneath the racks to allow the cooling air from the floor to cool the rPDUs mounted on the racks. The cooling air is often also filtrated by the CRAC/CRAH units to reduce the humidity level within the racks.
Some conventional racks for rPDUs are also provided with temperature and/or humidity sensors to monitor the temperature and/or humidity levels within the racks. When the temperature and/or humidity level within the racks reaches certain pre-determined threshold, the cooling and/or dehumidifying parts of the CRAC/CRAH units may be operated to reduce the temperature and/or humidity levels to prevent potential malfunction of the electronic devices mounted on the rack that may be caused by excessive temperature or humidity level inside the racks.
However, it has been a challenge to effectively and efficiently manage the energy usage for providing a suitable working environment inside a computer room. For example, electrical power distribution and usage provided through the rPDUs and by the electronic device mounted on the racks will generate heat inside the racks, so it is necessary to provide and circulate adequate flow of cooling air through the racks so that the electronic devices will not over heat. But cooling and circulating the air flow use energy in the form of electrical power that run the CRAC/CRAH units, and excessive cooling and circulating of the air flow will cause unnecessary energy usage.
Certain indices have been introduced in the industry to describe and measure the airflow and cooling performance of data centers. For example, Rack Cooling Index (RCI®) and Return Temperature Index (RTI®) have been introduced to measure the overall rack cooling effectiveness and the overall rack air-management performance, respectively. It is noted that RCI® and RTI® are registered trademarks of ANCIS Inc.; however for clarity purposes they will be referred to hereinafter as RCI and RTI without the trademark symbol (®).
The RCI index has two parts, RCIHi and RCILo, describing respectively the computer room temperature environment at an upper threshold and lower threshold of a safe temperature range. For example, for a rack system arranged in an indoor environment such as a computer room, an industry recommended safe temperature range may be between 18-27° C., and an industry maximum allowable safe temperature range may be between 15-32° C.
The RCIHi and RCILo are defined as follows:
                              R          ⁢                                          ⁢          C          ⁢                                          ⁢                      I            Hi                          =                                            (                              1                -                                                      Total                    ⁢                                                                                  ⁢                    Over                    ⁢                                          -                                        ⁢                                          Temp                      .                                                                                                  Max                      .                                                                                          ⁢                      Allow                      .                                                                                          ⁢                      Over                                        ⁢                                          -                                        ⁢                                          Temp                      .                                                                                  )                        ·            100                    ⁢          %                                    [        1        ]                                          R          ⁢                                          ⁢          C          ⁢                                          ⁢                      I            Lo                          =                                            (                              1                -                                                      Total                    ⁢                                                                                  ⁢                    Under                    ⁢                                          -                                        ⁢                                          Temp                      .                                                                                                  Max                      .                                                                                          ⁢                      Allow                      .                                                                                          ⁢                      Under                                        ⁢                                          -                                        ⁢                                          Temp                      .                                                                                  )                        ·            100                    ⁢          %                                    [        2        ]            Where:                “Total Over-Temp” is the sum of the over-temperatures (over an upper threshold of the safe temperature range) across intakes of all racks;        “Max. Allow. Over-Temp” is the maximum allowable over-temperature for the electronic devices mounted on the rack system to operate safely;        “Total Under-Temp” is the sum of the under-temperatures (below a lower threshold of the safe temperature range) across intakes of all racks; and        “Max. Allow. Under-Temp” is the maximum allowable under-temperature for the electronic devices mounted on the rack system to operate safely.        
For a computer room with a total of M number of racks each having N number of rPDUs for providing and distributing electrical power, the RCIHi/RCILo indices may be calculated as follows:
                              R          ⁢                                          ⁢          C          ⁢                                          ⁢                      I            Hi                          =                                            [                              1                -                                                      ∑                                          (                                                                        t                          ij                                                -                                                  t                                                      max                            ⁢                                                          -                                                        ⁢                            rec                                                                                              )                                                                                                  (                                                                        t                                                      max                            ⁢                                                          -                                                        ⁢                            all                                                                          -                                                  t                                                      max                            ⁢                                                          -                                                        ⁢                            rec                                                                                              )                                        ·                    M                    ·                    N                                                              ]                        ·            100                    ⁢          %                                    [        3        ]                                          R          ⁢                                          ⁢          C          ⁢                                          ⁢                      I            Lo                          =                                            [                              1                -                                                      ∑                                          (                                                                        t                                                      min                            ⁢                                                          -                                                        ⁢                            rec                                                                          -                                                  t                          ij                                                                    )                                                                                                  (                                                                        t                                                      min                            ⁢                                                          -                                                        ⁢                            rec                                                                          -                                                  t                                                      min                            ⁢                                                          -                                                        ⁢                            all                                                                                              )                                        ·                    M                    ·                    N                                                              ]                        ·            100                    ⁢          %                                    [        4        ]            Where:                i=1, . . . , M (number of racks)        j=1, . . . , N (number of rPDUs in a rack)        tij is the intake temperature of the jth rPDU in the ith rack;        tmax-rec is the maximum recommended intake temperature (e.g., 27° C.);        tmax-all is the maximum allowed intake temperature (e.g., 32° C.);        tmin-rec is the minimum recommended intake temperature (e.g., 18° C.); and        tmin-all is the minimum allowed intake temperature (e.g., 15° C.).        
The RTI index is defined as follows:
                              R          ⁢                                          ⁢          T          ⁢                                          ⁢          I                =                                                            [                                                      T                    Return                                    -                                      T                    Supply                                                  ]                                            Δ                ⁢                                                                  ⁢                                  T                  Equip                                                      ·            100                    ⁢          %                                    [        5        ]            Where:                TReturn is the temperature of the return airflow;        TSupply is the temperature of the supply airflow; and        ΔTEquip is the temperature rise across the rack.        
These indices are not completely independent of one another, reflecting the challenge of improving both the effectiveness and the efficiency of the energy management system. For example, reducing air temperature and increasing airflow in a rack will increase the rack cooling effectiveness and therefore improve the RCI, but it will also increase energy usage for cooling the rack and therefore reduce the overall rack air-management performance, resulting in a poor RTI.
One of the results of a poor rack air-management performance is low energy efficiency. For a computer room, the total power consumption is the sum of the electrical power distributed to the electronic devices by all of the rPDUs mounted on the racks in the computer room and the electrical power used by its CRAC/CRAH unit in air-management, and the energy efficiency may be calculated as
                              Energy          ⁢                                          ⁢          Efficiency                =                                            Power              ⁢                                                          ⁢              distributed              ⁢                                                          ⁢              by              ⁢                                                          ⁢              all              ⁢                                                          ⁢              rPDUs                        ⁢                                                                      Total            ⁢                                                  ⁢            power            ⁢                                                  ⁢            consumption            ⁢                                                  ⁢            of            ⁢                                                  ⁢            the            ⁢                                                  ⁢            Computer            ⁢                                                  ⁢            Room                                              [        6        ]            
There are still shortcomings existed in conventional power and energy management systems that affect the energy efficiency of the computer rooms. Operators and/or managers of conventional power and energy management systems who are in charge of providing and maintaining a suitable working environment in a data center often face a series of questions related to the control and operation of the CRAC/CRAH units, such as:                Is the chiller of the CRAC/CRAH unit cooling the air circulation effectively? Is there a need to reduce the air temperature? Is the electronic device in the racks safe at the current temperature?        Is the dehumidifier of CRAC/CRAH unit maintaining the humidity level inside the racks effectively? Is there a need to reduce or increase the humidity level? Is the rPDUs in the racks safe at the current humidity level?        Is the fan of the CRAC/CRAH unit circulating air inside the racks effectively? Is there a need to raise the fan speed to increase the airflow?        Is the CRAC/CRAH unit working efficiently? Are there ways to improve the overall air-management performance to improve the energy efficiency? What is the expected energy saving?        
The answers to these critical questions directly affect not only the effectiveness of the control and operation of the CRAC/CRAH units for the well-being and safety of the electronic devices in a data center, but also the efficiency of the energy usage and conservation for the overall air-management performance. Yet existing conventional power and energy management systems do not provide sufficient and effective tools and procedures for the operators and/or managers of the system to answer these questions in real-time and to find and provide adequate solutions to the challenging objectives.
Therefore it is desirable to provide a new and improved system and method to safely and effectively use and save energy for data centers using rPDUs.